1. Field of the Invention
The present invention relates to a power converter, and more particularly, to a control circuit of a power converter.
2. Description of Related Art
A variety of power converters have been widely used to provide a regulated voltage and current. In order to precisely control the output current, traditionally a current detection and control circuit is equipped at the output of the power converter. However, a considerable power loss is normally consumed due to the output current detection, particularly as the output current is high. Besides, this output current control circuit takes a space of the PCB (print circuit board) and increases the cost of the power converter. Thus it is desirable to provide a control circuit that combines with a switching control circuit of the power converter for the output current control. Furthermore, the control circuit can be combined with the switching control circuit as one integrated circuit, which dramatically reduced the space and cost of the power converter.
Many prior arts are developed to control the output current of the power converter, such as “Control circuit for controlling output current at primary side of a power converter” by Yang, et al., U.S. Pat. No. 6,977,824; “Close-loop PWM controller for primary-side controlled power converters” by Yang, et al., U.S. Pat. No. 7,016,204; “Switching control circuit with variable switching frequency for primary-side-controlled power converters” by Yang, et al., U.S. Pat. No. 7,061,780. The power converters of the foregoing prior arts operate at a predictable switching frequency, which facilitates the detection of the output current. However, these prior arts are unable to apply to power converters with changeable switching frequency such as resonant power converters.